Cellular defenses against the toxic byproducts of oxidative metabolism have long been considered an important factor in a variety of disease states, as well as the normal processes of aging. They are of particular importance in the central nervous system because of the very high rate of metabolism in these tissues and their essentially non-regenerative nature. Since its discovery over 30 years ago, there has been increasing awareness of the central role played by the enzyme glutathione peroxidase (GPx) in the cellular antioxidant system. Although GPx has been extensively characterized in other tissues, little is known of its structure, distribution, mode of action, or interaction with other metabolic pathways in the brain. The goal of this study will be to clarify the role of GPX in the brain with respect to each of these factors. These investigations will be carried out both in isolated brain preparations, and viable cell cultures of neuronal origin as model systems to study the effect of oxidative stress on the integrity of neural tissues. A particular focus of mechanistic studies in this proposal will be the interaction of GPx with monoamine oxidase (MAO), as the principle metabolic enzyme in degradation of the amine neurotransmitters. This oxygenase appears to be a major source of potentially cytotoxic H202 in the CNS and there is evidence that it is functionally coupled to GPx as a detoxification pathway. Specifically the following lines of experimentation will be pursued: (1) MAO, GPx and the other major enzymic components of the antioxidant system in the CNS (glutathione reductase and superoxide dismutase) will be localized by brain region and cell type by means of both biochemical assays in dissected brain regions and immunohistochemical staining of sectioned brains. (2) The two isozymes of GPx found in the cytosol and mitochondria will be isolated, purified and characterized from rat brain. (3) Specific inhibitors of GPx other components of the antioxidant system will be used to investigate the effects of oxidative stress induced by biogenic amine metabolism or chemical oxidants on cellular function and integrity in brain preparations and viable cell cultures. (4) The methods used in "(3)" will be applied to investigation of the role of the antioxidant system in the mechanism of cell killing by a specific neurotoxin of widespread current interest, the compound MPTP which induces a Parkinson syndrome in humans and primates.